MP66 & Compressor Overheating

[Intermez]

Working on an MP66 cold plate system that the previous company walked away from. System was R12, last company put in 409. Wouldn't pull below 0 cold plate temp, cold plates freeze at -10. I put in MP66. Had high compressor outlet temps and had to run compressor superheat very low to get below -10. Just put in a liq/suc heat exchanger trying to raise comp superheat.........well it did. Up to 80 to 100 degress. Tried various evaporator superheats, no luck, still see very high comp outlet temps. Been trying various settings until outlet temp gets to 225, then shut it down to cool. Looks like I made things worse, as usual. What am I missing? Only thing I can think of it that I need an equalized TEV. Don't know what the pressure drop is across the plates but there's a fair amount of tubing in them (probably 60 ft. of 3/8). Help!!!!!

Thanks, Kevin

[Peter_1]

Some questions Kevin: what's a MP66 cold plate system?

Cold plates freeze at -10(°C?)So it's for a coolin application. Right?

Had high compressor outlet temps and had to run
compressor superheat very low to get below -10.
How did you do this? I can't follow you. Superheat has nothing to do wit reachinhg an evaporating temperature.

Just put in a liq/suc heat exchanger trying to raise comp superheat
What was your intention by installing a HA?

80 to 100 Degrees SH
It's more like an egg boiling device.

Isn't it normal that with high SH you will have high discharge temperatures, don't you think?

Most probable cause: defective TEV, mositure in system, blockage in the TEV,...
Cold plates are many times installed with a MOP TEV, so high SH at start up is then normal.
You must give it some time.

You said you probably need a TEV with external egalisation.
How many plates do you have and what type of compressor?

Try to use SI units between brackets please

[Intermez]

Peter,

Thank you very much for your reply. I'm going nowhere on this and appreciate your input.

Plates are -10F freezing point

I had to run very low superheats to get enough ***** into the compressor to keep discharge temp below 225F so that I could run it longer than 4-5 min. When I did this, I could get the plates to cool and after a while (20-30 min) I could then increase the compressor superheat to normal values of 20-30 degress while still keeping exhaust temp below 225F. Then I put in the heat exchanger and became even dumber in the process.

My hope on installing the heat exchanger was that with cooler liquid (about 70F versus 105F) that I could get the plates to pull down faster and that with normal superheat I sould stay under 225F. I wasn't expecting the gas temp go up 100 degrees or more. Obviously now with the heat exch., the overheated discharge is due to the high inlet temps.

I can definitely fry eggs on the compressor if I leave it run.

Small system, 1.5HP hermetic, three plates in series. Water cooled, 85F cooling water temp. The TEV is standard, not an MOP. Once I get the thing over the hump it starts to make more sense, it's just getting to the hump......

Owner said that with R12, he was able to pull plates down to -15F in about 1.5 hrs. With all the mess I've made, I'm happy to see them at 0F in three+ hours

Thoughts, I know I'm probably missing something obvious but my mind is fried from sitting around a hot compressor.

Many thanks, Kevin

[Peter_1]

Kevin, I think I can say we have some experience with this.We're even making the plates ourselves.

Easy, -10°F= -23°C.

The HE isn't the cause of your problem neither the solution of it. I never used a HE in my whole career because I don't believe in it. If you look at it pure thermodynamic, it's a zero operation.

It had worked in the past, so you must focus on something else.

Have no experience with MP66, is this a drop-in for R12?

On the startup, high SH is normal but the values you give, 225°F( I did the conversion myself 107°C) seems indeed too high.

What type of valve is installed and what orifice is in it?

I shouldn't believe what your customer is telling you, 1,5 hour is impossible. You allways have to listen what they tell you but take the some distance and try to figure out if it make sense what they tell you.

Never believe them for 100% but their story could give you valuable information, even if your customer is not a tech.
I don't know how long you're in the business and how much aexperience you have but that's the advice I gave my son.

Most systems we install, also 1,5 HP hermetic and plates on -10°C(13°F which goes even much faster then your plates) takes almost 8 hours to cool down. You can calculate this yourself by calculating the latent heat of the mix in the plates.
It will soon reach the eutectic temperature but it takes many hours to solidify the eutectic mix.

Change your valve to a Danfoss TE 2 (an external equalization isn't needed for only 3 plates) or a similar one with same capacity, mount an orifice 1 in it, probably a 2 and replace the drier.
I'm almost sure it will work, but give it some time (speaking in terms of some hours) to remove all the latent heat out of the mix.

Install also a SV, electrical parallel connected with the compressor or even better, pump it down. Otherwise all the refrigerant will migrate to the plates at standstill and this is something the compressor doesn't like at all.
Don't use also a thermostat like so many do but let it cut out on a pressostat, set at +/- 6 to 10 K below the eutectic point. Give a DP so that it starts back around the eutectic point.

Give me some more information regarding my questions about
MP66
Type compressor
Type TEV

And now you or others have to help me ;) :
Is pressostat a correct English expression?
Is it eutectic or eutectical solution?
Is it ourself or ourselves?
Is it external equalisation or egalisation?

[Intermez]

Peter,

Wow, you're the first one I've talked with that knows cold plates.

I can help with some of the questions:

pressostat - Probably European, being form US, I call it a pressure switch.

eutectic - this is definitely correct, the thermodynamic term is eutectic point.

ourself/ourselves -- if you're talking about you individually, it's ourself, if you're talking about your company, it's ourselves.....from the wife, much better english tahn mine.....

It's equalisation, equalzation over here.

To the less important stuff,

MP66 (R401B) is a low temp R12 replacement. It's a blend with 8 degree glide. Requires oil change from mineral to AB. It's the only thing out there that dosen't require POE and works for low temp applications as far as I know.

Compressor is a Tecumseh, low temp, have to look up the model number if that's useful.

TEV is a Sporlan GF1Z, low temp, 1 ton capacity.

Startup superheat is around 100F. The 225F is the compressor discharge temp. which is where the first problem is. Compressor superheat really never drops much below 80F with heat exchanger. Ran it down to 10F (before I installed the heat exchanger) in order to keep discharge temp below 225F.

I think customer was talking about average daily run times to pull the plates down, not total pull down.

"Install SV", not sure what you mean, but there is a liquid line solenoid to stop plate flooding on turn off. System has both temperature and pressure switches, I agree on using pressure switches as you said. Not sure why there is a temperature switch also. Hasn't been an issue because I haven't gotten the plates low enough to worry about that yet.

Installed new liquid and suction side filter driers (first thing I did on this job)

Experience, not nearly enough, only about 5 yrs, mostly residential with a little commerical supermarket , first time working with low temps and cold plates.

You mentioned in your first note a defective/clogged TEV. Will pull it out tomorrow and check. Just doesn't seem like there is enough refigerant flow.

Once again, many thanks, really appreciate the help and someone who knows what they are doing!

Kevin

[US Iceman]

HI Kevin,

Welcome to the RE forums. I see you have already met Peter.:D

Are the plates you are using made by Dole?

Here is some information that may be worthwhile:
http://www.doleref.com/Assets/Sales%20Catalogs/Kold-Hold%20Catalog.pdf (+2 MB)

The plate systems I remember working on were all R-12, however it did take almost all night for them to re-charge completely. Certainly not 1-2 hours.

Peter was right on the money when he said listen to the customer, but don't believe all of it.

The systems I worked on had normal TXV's (no MOP) but they did use a crankcase pressure regulator (CPR) valve to keep the compressor suction pressure down to a reasonable level until the plates started to cool down.

I suspect an internally equalized TXV will work OK. The length if tubing in the plates is not too long. It just sounds like a long run.

How warm are the plates when you try to start the refrigeration system?

Let's start with the easy stuff before we get too excited about system problems.

[Intermez]

Good morning Iceman,

Thanks for the welcome. Looks like a great place, after browsing many threads, really impressed with knowledge/humor here.

Can't tell the plate manufacturer but after looking at the Dole info I doubt if they came from Dole. Just don't look at all similar.

Plates are typically about 10F when I start up. In the PM I'm able to run the compressor in 5 min intervals, letting things cool between runs, and get it down to around 0F so it can hold till I get back the next day.

Getting meaningful readings in this mode is difficult as things haven't stabilized and all the readings are moving.

Appreciate getting back to the easy stuff. Maybe you can spot something that I've obiviously missed. All I've learned dosen't seem to be working.

Thanks, Kevin

[Intermez]

A little more information:

Decided to try a few things again. Here's what happened. Was able to stabilize things with the compressor exhaust temp around 216F. Saw it vary +/- a few degress as TEV cycled (I think). Read -6 psi (about -12 in Hg) for a -40F vapor temp. Plate outlet temp -30F, superheat 10F. Opened TEV one turn.....thinking this would decrease superheat a bit, raise pressures to a more normal level. Within 1 minute of doing this, exhaust temp rose quickly to 225F and heading higher. Shut system down. Plates are about 0F.

Clogged TEV???? Pulling it now to check.

Many thanks once again, Kevin

[Intermez]

Just finished checking the TEV. Nothing in inlet screen to speak of. Removed TEV, heated it up some to remove any signs of moisture, reinstalled and evacuated. Restarted system, same results.

I'm about to throw in the towel.............

Kevin

[Peter_1]

SH seems +/- normal, what's your HP and SC?

6 psi = +/-0,4 bar, so this seems also OK.

Was the original pressure switch setting not set below atmospheric pressure?

There's a chance that non condensables have entered in the system.

225°F = +/- 108°C, far too high.

Remove all the gas, vacuum it and look if vacuum holds, to be sure you have no leaks and refill it with a new charge.

How I do it: fill the gas in an empty, dry and clean cylinder. While the systems vacuums for the needed time, let standstill the cylinder with the recovered gas so that the liquid gas and the non-condensables separate well.
Take another empty cylinder and vacuum it a little bit. Release or purge the gaseous refrigerant from the first cylinder - and the non condensables) from the recovery cylinder to the second one. Most of the non-condensables are now in the second cylinder. Refill it with the recovered gas.

Another method if you have to turn your cylinder to fill with liquid refrigerant.
Weight the empty cylinder precisely
Recover the whole charge again in this cylinder and weight the amount of refrigerant in the cylinder.
Turn it upside down and let it stand there while vacuuming.
Refill it in liquid form but let some liquid (+/- 200 gr) in the cylinder, acting as a liquid seal so that the n,non-condensables can't enter the system.

Was this explanation clear and do other posters use a similar workmethod? Feel free to comment.

The cylinders with a tube downwards for charging liquid while standing upright are more difficult to use because you're never sure that the tubes goes straight to the bottom of the cylinder.

[Peter_1]

See our messages crossposted each other. Have you refilled with the original gass?
You're sure you use the right gass?
HP and SC are valuable readings you have to make.
I'm doing this (temperature readings) mostly with my bare hands, especially with R-12 drop ins. Try to learn and to use this technique.
Isn't there a possibility that the original gas filling has decomposed?

[Peter_1]

Just finished checking the TEV. Nothing in inlet screen to speak of. Removed TEV, heated it up some to remove any signs of moisture, reinstalled and evacuated. Restarted system, same results.

I'm about to throw in the towel.............

Kevin
It's not because you don't see moisture or debris that it's functioning the right way. There can also be a possibility that the gas charge of teh bulb is partially gone.

But I think not in your case because the valve regulates for its 10K SH.

Don't throw the towel in the ring now, these are situations you will learn the most of and especially the pride you will feel if you finally have solved the problem. And not to forget, a satisfied customer.
This is the learning process many of us did so many years.
You're close to solve the problem now, don' give it up now.

Can others help in this issue?

[US Iceman]

Has any of the components been replaced from the original installation? Do you have the same compressor, TXV, etc?

Second point... With the exception of one post all of the data you are suppying to us is temperatures. You need both pressure and temperature to find problems.

What is the suction pressure and discharge pressure (don't call that the exhaust pressure, you will only confuse others).

What is the suction temperature and discharge temperature? Both of these you can find with a thermometer at the compressor service valves. About 6 inches away from the valves should be fine.

Next question: What kind of condenser do you have? Air-cooled I suspect. Does it have any dirt in it? Look at both sides of the condenser coil. Sometimes you have to blow them out with compressed air.

Next question: Are there any regulating valves in the suction line between the cold plates and the compressore suction service valve?

How was the system charged with MP66? If you charged it with gas, you will have some problems. That is what Peter was describing I believe.

What is the liquid line temperature after the receiver, or condenser?

[Peter_1]

USICeman, indeed, charegd gasseous MP66 or the original charge ahd a small leak and some of the components went out the solution.

Indeed, a crankcase pressure regulator.

Intermez, this isn't meant personally but so many techs forget that a system never can't be proper analysed if you don't have some basic readings: LP, HP, SC, SH, discharge temperature, liquid temperature, suction temperature. All these must fiit together and if there's one or more jumping out the row, then mostly you can better pinpoint the system.

I wrote an article for the Belgium C&C which describes the technique of 'feeling' temperatures with your hands. It's of course written in Dutch.

[US Iceman]

Hi Peter,



I wrote an article for the Belgium C&C which describes the technique of 'feeling' temperatures with your hands. It's of course written in Dutch.


This is something a lot of people never learn to develop. I learned this from my grandfather ;).

Of course you do have to learn which pipes are the most likely to very hot too.:eek:

I think you have said in the past to spit on them. It may appear to be a unsanitary service method, but it works, right?

Once he gets use to this method, he can probably know what the problems are before the gauges are installed.

One other question... Why is the plate temperature trying to be kept at -30F (-34.4C)? This is a lot colder than any plates I have seen or worked on. There was a mention of 12 in. Hg, which sounds very low to me.

[Intermez]

Thanks guys for the input. I have been doing most of the things you mentioned. This answer might be long but here's all the data:

Original installation:

1.5 HP Tecumseh hermetic compressor
Liquid and suction accumulators
Water cooled condensor
R12
Mineral Oil
Don't have any readings for this system. Apparently worked for years.

2nd installation by another company.

Hardware all the same except:
Changed to a Sporlan GF1Z TEV, changed system to R409a
There are no pressure regulating devices of any sort in the system other than the TEV.
They never got it to work.

3rd System

This is where I came on the scene. From all I've read and input from others, all said that R409 wouldn't get below 0F very effeciently. All suggested going to R401B (MP66) because of -10F freezing point of plates. This necessitates at least -20 or -25F evaporation temps for good heat transfer between the refrigerant and brine in the plates.

Here's what I did.

Verified that the Sporlan TEV currently installed was
acceptable for R401B. Recovered system completely.
Cleaned system with solvent, removed as much oil as I could from the compressor. (I didn't want to assume that the previous company had correctly changed from mineral oil to AB.) Added AB oil, evacuated and then charged system with R401B.

Here are the readings I had at the time:
HP 160psi
Discharge temp climbed to 225F within 5min of startup.
Evaporator pressures and temps were continuously decreasing as system was still pulling down. Evaporator pressures went form +10psi down to at most -11 in Hg. The low end pressure varied bacause I was trying various superheat settings to keep the discharge temperature down low enough to keep the system running so I could get some stable readings as a starting point. (Assuming more ***** flow, lower superheats would cause more compressor cooling). During this process I found that if I set the superheat very low, and the corresponding compressor superheat low (it ran about 10F) that there was enough cool ***** getting to the compressor that I could keep it running long enough so that discharge temps would come down to aroun 200F. At that point I would try increasing superheat at the evaporator to around 8 degress and the discharge temp again would starting to rise to 225F+.

During all this I was running SC pressures from +4 psi down to -8in Hg. Compressor inlet temps of course varied with the particular setting I was trying, but were around 0F plus/minus 15 degrees, Whatever I tried couldn't find a balance.

2nd step:

For some reason I thought I'd install a liq/suc heat exchanger, hoping that the cooler liquid temps entering the evaporator would help things pull down quicker, allowing the system to stabilize faster. Didn't work because with the heat exchanger, compressor inlet temps rose to 60F to 80F and exhaust temp were obviously high. When I installed the heat exchanger, recovered the R401 and put in a completely new charge.

3rd Step

Checked TEV as best I could. First heated TEV with hair dryer to see if I could unfreeze any possible moisture. No effect. Removed TEV to check inlet screen. Nothing found. Checked TEV operation with 100 psi nitrogen, bulb both cold and hot. TEV seemed to function. Replaced TEV. Evacuated and started system; here's the reading I got:

RUN 1
Sc (evaporator outlet pressure) -4 in Hg
Evaporator discharge temp -19F
Plate temperature -2F
Superheat 8F by my caculations
HP 162 psi
Compressor suction temp 70F
Discharge temp 225F
Condensor Refrigerant Out Temp 105F
Condensor cooling water inlet temp 85F
Condensor cooling water outlet temp 94F

These readings were after 7 min of run time. Compressor had been cooled to ambient (90F) before starting. Plate temperature dropped 2F during the run.

RUN 2

Next tried increasing superheat, 1 turn in on TEV

SC pressure -11 in HG
Evaporator discharge temp -24
Superheat around 16F
Everything else about the same, run time before reaching 225F was 12 min. HP 160psi, compressor suction temp 68F.

RUN 3

Just ran it one last time after colling the compressor. MAJOR CHANGE: Reset TEV to where it was for RUN 1 above. Immediately on startup compressor suction temp dropped quickly to around 30F, gradually down to 8F and then back up to 38F. Forst building on compressor suction valve, then disappearing. Did not hear any sign of liquid slugging (due to accumulator I would assume) Compressor discharge temp rose to 217F down to 200F and then back up to 225F. Run time 23 mins.
At 214F discharge temp the readings were:

Evaporator discharge pressure -2 in Hg
Evaporator discharge temp -28F
Superheat 0 to slightly negative
Compressor suction temp 38F
HP 155psi
Condensor discharge temp 100F

I added two turns of supreheat (should be 4 or 5F increase). By the time I got to the compressor to look at the discahrge temp, it had risen to 224.3 and was climbing quickly.

Let compressor cool, started another run, and once again saw 80F compressor inlet temps. Shut things down and went home.

Question: What would have caused such a drastic change in compressor inlet temps?

Sorry this took so long, hope there is enough pressure data. Will be more careful in the future to write down everything! Hope I answered all the questions, mind is sort of fried at the moment.

THANKS, Kevin

[US Iceman]

First of all here is a link to the pressure/temperature tables for this refrigerant (and others).

http://refrigerants.dupont.com/Suva/en_US/pdf/k10909.pdf

Let's start with this example...



RUN 1
Sc (evaporator outlet pressure) -4 in Hg
Evaporator discharge temp -19F
Plate temperature -2F
Superheat 8F by my calculations
HP 162 psi
Compressor suction temp 70F
Discharge temp 225F
Condenser Refrigerant Out Temp 105F
Condenser cooling water inlet temp 85F
Condenser cooling water outlet temp 94F


First some questions... What is Sc?

If the evaporator outlet pressure is 4 in.Hg (you do not have to use the minus symbol here, the vacuum already shows the pressure is negative)

4.2 in.Hg = -26F according to the table posted above

If the temperature of the suction line leaving the plate is -19F (you called it evaporator discharge).

-19F minus -26F = 7 degrees of evaporator superheat. That's not too bad if your numbers are correct.

Now, your suction temperature at the compressor is 70F. If we take the 70F suction temperature minus the -19F, you have over 89 degrees of superheat added to the evaporator superheat of 7 degrees. That's 96 degrees of total superheat at the compressor. That's enough right there to make the compressor very hot.

Looking at a pressure/enthalpy diagram that would put your discharge temperature around 250F or so, which means you are about right were I would expect with this much suction superheat.

The discharge pressure and liquid temperature leaving the condenser look about right. As does the condenser water temperature range. In other words, these look reasonable.

It would be nice to know the suction pressure now. The suction pressure SHOULD be close the evaporator outlet pressure if nothing else is wrong. A little lower, but not much.

At this point without the compressor suction pressure, I have to guess...

Somewhere between the outlet of the evaporator plate and the compressor suction service valve something is adding about 90 degrees worth of superheat to the suction line.

Or, something is causing an extreme pressure drop in the suction line in this area. Very high pressure losses in the suction line will appear to be only superheat. But since we don't have the suction pressure, well...:(

If the suction line is not crimped, or full of solder, then you more than likely have something adding a lot of heat to the suction line.

I suppose the liquid line could be crimped or blocked to some extent, which could cause the liquid to flash off before it enters the TXV. Does the TXV sound like it is hissing, or gurgling a little? Is the TXV cool or warm?

What are the motor amps? Are they close to something that agrees with the compressor nameplate full load amps (FLA)?

You have an interesting problem that's for sure.:confused:

[Intermez]

Iceman,

Thanks again. Someone, perhaps Peter used the term SC, I took this to mean suction. Anyway that's what I meant.

I measured the pressure drop from the evaporator outlet to the compressor suction port a few times. The most I have ever seen is 2psi.

The superheat added to the suction line is coming from the heat exchanger. However, if you got far enough into my novel, what I don't understand is the one run (think I called it Run 3) where the suction temperature dropped to 30F quickly after start up, then over the next 5 min. down to 8F and then gradually back up to 40F. This is with the heat exchanger in place. Unfortunately did not have a guage at the compressor to read the pressure there at the time. With the next start up of the system, the suction temperature was back up to the 70 to 80F range. I'll measure the pressures at both the evaporator and suction port at the same time tomorrow.

I hear no sign of any gas passing through the TEV, no hissing, gurgling, etc. Amps drawn by the compressor start up near FLA of 14, gradually drop off to below 9 amps. Sorry about the -4 in Hg. My background is electrical, I add a - sign to anything that goes below zero.

By the way, before I put the heat exchanger in the system, the suction temps were lower but still had high discharge temps.

Keeping the towel handy, but like you said, I want to somehow solve this, and once again learn how much I don't understand..

Kevin

[Peter_1]

I'm thinking now on something: we had a service-call 2weeks ago on a eutectic plate.
The fed-troughs were cracked.
The explanation will be too long for the moment now but the fed-trough exploded while I was soldering it. I thought that moment I lost my hearing.

The tube is a 1/2", fed trough a 5/8 to prevent cutting on the sharp edges of the stainless steel plates. We always make stainless steel plates.

You can see on the pictures that the outlet of the plate that the inner pipe is almost completely flat squeezed.
Before I soldered it and before it exploded, both tubes looked similar, so it was squeezed inside the 5/8".

Happy now I took a picture of this 'stupidity' :o
And perhaps strange to say but if it hadn't exploded, I never should have seen this fault.

I haven't checked in the pressure/enthalpy chart if your pressing/temperature readings are correct and correspond with each other but USIceman did it already, so his conclusions will be right: a blockage.

Solder a schradervalve between plate 1 and 2 and between 2 and 3. If everything is OK, then all readings, including the suction pressure at the compressor should be the same.
You then better can locate the blockage in your system.

[Intermez]

Good Morning Peter,

That looks like it was quite an explosion. I take it you fill the plates with hydrogen before soldering.

Any idea what happened to cause it to blow like that?

I'll put the Schrader valves in today. Unfortunately there's no way to get one in right at the TEV outlet, but can get at the other two points.

What do you think could be causing a blockage if it's not something like a crushed tube? I would think it would take a lot to block a 3/8" tube.

Thanks!, Kevin

[Peter_1]

What do you think could be causing a blockage if it's not something like a crushed tube? I would think it would take a lot to block a 3/8" tube.
Well, freezing water has squeezed my tube of 1/2.

Could also be a foreign object of the previous tech.

Found once - +/- 10 years ago - a small piece of cloth in the outlet of a receiver of a milktank. It must been there since fabrication in factory.
You should have seen the farmer's face when I grinded open the reservoir. He couldn't believe that I could know that something was inside the reservoir.

The explosion I had was trapped water between the 1/2" and 5/8 " tube which made very fast steam while I was heating it. My wife was inside the home and she ran to me when she heard the explosion. I was soldering it in place in a small closet.

[US Iceman]

Well it seems to me that the guys who worked on this before did something that really messed this up.



Could also be a foreign object of the previous tech.


That is what I'm thinking. Unless, if you can make sure the suction line pressure loss is no more than 2 psi from any plate outlet connection back to the compressor.

I have trouble believing the suction line heat exchanger is adding almost 90 degrees of superheat with a liquid line temperature of only +/- 105F (40.5C). Usually you only find about 10-20 degrees of superheating, and that is high, in my opinion.

On the heat exchanger installation I have a question. There should be four connection on this. Two are for the suction lines; one inlet & one outlet.
The other two lines are for the liquid line; again, one inlet & one outlet.

Are you sure the two smaller connections are connected to the liquid line? (the small line coming out of the condenser. You may have a receiver, so the two connections should be in series with this line, after the receiver.)

You did not by any chance connect the discharge into these two connections did you? To get that much superheat (+/-90 degrees) this is about the only way I can see this happening.

Either that, or someone installed a hot gas bypass for some strange reason???

Without being able to see anything we have to go on your descriptions and the data you provide.

You mention the suction temperature starts normal in some cases then quickly rises. The plates could hold enough residual refrigerant to refrigerate normally for a short while. This would quickly evaporate when the compressor is running, and then the high temp's could start.



I hear no sign of any gas passing through the TEV, no hissing, gurgling, etc


Take a long screw driver and place the metal end on the TXV. Put your ear on the plastic handle. Instant stethoscope! You should be able to hear something.



I take it you fill the plates with hydrogen before soldering.


God forbid you should do something like this.:eek: That would be an explosion you would not walk away from.

Use free-flowing nitrogen, nothing else. The nitrogen has to flow in and out of the system in a completely unrestrained manner.



My wife was inside the home and she ran to me when she heard the explosion.


Peter, she did not drop any of her good tea cups did she?

Restrictions come from funny places... I have heard about about a lunch box, a piece of wood, and a bag of bolts being inside of a large suction line in an ammonia system. Strange things happen.:o

[Intermez]

Thanks guys,

Finally convinced the customer that I couldn't keep on working on this thing without emptying it. He very reluctantly agreed. Now in the process of deforsting the plates. Will add Schraders for better measurements. While things are defrosted, any recommendations on flushing solvents? I've only used a liquid type followed by nitrogen. Want to do a very thorough job before I put things back together.

Heat exchanger was installed correctly. Might put a sight glass directly before the evaporator temporarily to look for any gas bubbles. Will also do the screwdriver check. There is no hot gas bypass valve installed. Probably won't have any news tomorrow, unless I find a mouse or the like in the suction line.

Kevin

[US Iceman]

Why are you trying to flush the system? That could create more problems than currently exist.

[Peter_1]

Kevin,

Perhaps not such a bad idea that you print out this whole thread - edit it perhaps a little bit - and let it show to your customer.

He will then see that you've taken a lot of work aside the work he saw to solve his problem.

And also to let him know that a lot of other techs worldwide have helped you and him.
He perhaps will realise that the problem was not that easy and that the reason for the problem was already in the system when he called you.

If you find a mice, I want a picture of it...in close-up. :D

But think also once on the restriction I gave you on the picture.

If you're self-employed, then you can make an arrangement and say that he only has to pay some hours but not everything.

I should not flush it like USICeman suggested - a too time-consuming job and too expensive to perform - just blow it through with dry nitrogen.
The main purpose now is finding a restriction.
And if you find something, don't remove it before you have it shown to your customer so that he's convicned that all your work was needed to solve the problem .

[Peter_1]

First some questions... What is Sc?

I used it for SubCool

[US Iceman]

I used it for SubCool


Stupid me, I should have realized this is what you meant. When I saw it with the suction pressure in his post, I did not think about that. :o

I'll try not to let it happen again...

[Intermez]

Peter and Iceman,

Will take your suggestions and back off on doing a flush. Will just use nitrogen.

Definitely like the idea of printing this whole thing out and giving it to the customer. You're right, I think he would be impressed with the high quality support that's out there and the thought and time given to this whole mess.

Hopefully will have some good news tomorrow. Will definitely be looking for wildlife in the suction line or around all the welds looking for explosive crimping of the lines. Couldn't beleive how long (9 hours) it took to get those plates above freezing. Eutectic cold plates are impressive.

Kevin

[Peter_1]

Now, your suction temperature at the compressor is 70F. If we take the 70F suction temperature minus the -19F, you have over 89 degrees of superheat added to the evaporator superheat of 7 degrees. That's 96 degrees of total superheat at the compressor
According to this statement, the restriction must be in the last piece between last plate and compressor (perhaps the liquid separator) and it all depends on the figures you've given are correct and we interpreted those the right way.

[Intermez]

Peter,

I understand what you mean. When I'm done with the plates will look again between the plates and the suction port.

I suspect though that there's a blockage in the plates. This could still account for the readings. How's this for a theory: Blockage in the plates, ***** flow very low. TEV able to set to correct superheat eventhough the flow is low. Since flow is low, heat picked up from heat exchanger & 30ft. or more of suction line, dryer, and receiver is able to raise the temp of the small amount of ***** in the line between the plates and suction port. Does this make sense? Only way to tell I guess, as was mentioned before, is various pressure measurements along the suction side.


Kevin

[Peter_1]

This could still account for the readings. How's this for a theory: Blockage in the plates, ***** flow very low. TEV able to set to correct superheat eventhough the flow is low. Since flow is low, heat picked up from heat exchanger & 30ft. or more of suction line, dryer, and receiver is able to raise the temp of the small amount of ***** in the line between the plates and suction port. Does this make sense?
Your way of thinking is correct Kevin.
Let us surely know what you've found or if you need more information.
Take your digital camera with you if you have one. Many can learn from this.

[US Iceman]

Low mass flow in the suction line could cause this. That is one way of explaining why the heat exchanger is adding so much heat to the suciotn gas.

I want to ask a "stupid question". Do the plates have individual expansion valves (one for each plate) or is one TXV feeding multiple plates?

If one TXV is feeding multiple plates, what the refrigerant distributor look like?

[Peter_1]

US Iceman, many of these systems are simply connected in line.
We had once a van with +/- 7 plates in line.

There's not that much copper in 1 plate.

There are some advantages of this is if you connect them in line:

1. You don't have to take care of making that every plate has the same pressure drop and that each plate is fed the same way
2. Less expensive then any other system
3. Only the last plate has to make the needed superheat. When each plate should have his own TEV, each plate need a certain unused section for superheating. So the plates are better cooled, more uniform.

Disadvantage: if a TEV brakes, then the whole system will shut down on LP. But this happens very seldom.

We even connected them in line through plates with a different eutectic solution (plates in the mussels stroage must have an eutectic point of -5°C, counter at -2°C to avoid freezing of the fish on the ice but making that the ice doesn't move while driving the van, the ice storage is kep at -8°C or -10°C,...).
While pulling all the plates below their own eutetctic point (we cut it out on LP on a corresponding temperature below the lowest eutectic point in the system), the plates with the highest freezing point where frozen a little bit to deep but as soon teh compressor is shut down, they fast rise to their eutectic point and stay their while melting.

But this did you know already, it's only shearing my experience with those just joined our métier like the French say.

[US Iceman]

Peter,

This is a really good discussion on system troubleshooting and system operation.

I hope the young guys are reading this.;)

[Peter_1]

And that they understand the logic behind all this.

[Intermez]

Good morning guys,

Well you were both right and the readings as well. No blockage in the plates. Disconnected each one separately, blew them out in both directions, seemed absolutely clear and only thing I got out was a few drops of oil. Now on to the rest of the suction side.

The three plates are connected in series with one TEV.

I did not mention previously, but part of my job was to separate the freezer and refrigerator sections and to install a second compressor for the refrigerator.

When I got on the job the system had the one 1.5HP compressor feeding the three freezer plates with one TEV, paralled with a second TEV feeding two refrigerator plates. Put in a second .5HP compressor and separated the refrigerator plates from the 1.5HP system. The new refrigerator system is running flawlessly.

The freezer problem was there with both the freezer and refrigerator plates paralled on the 1.5HP compressor. Verified this before I did anything by disabling the liquid line solenoid going to the refrigerator TEV.

Will get back with some good new today, I hope.

Kevin

[Peter_1]

Kevin,

Where were we both right regarding the readings?

If I understand you correct, there was no blockage at all in the plates?

But you said that the problemwas there when 5 (3 freezer and 2 cold room plates) were connected together. Is the problem then gone now?

I think you have to look in the piece between last plate and compressor.
Is liquid separator the original one? If newly installed, it perhaps was fit the wrong way (in/out and out/in)?

Important readings you have to make for us when system runs for an hour - don't look at the discharge temperatures and let it run that way - so that it is stabilised a little bit: temperature at outlet last plate, temperature in and out HE, temperature in and out accumulator and temperature and pressure at the inlet service valve on the compressor.

Is the 1.5 HP compressor a LP one or a HP one?
I suppose a LP because your current is max on startup and compressor goes beyond - temporarely - its limits.

[Intermez]

Peter,

Both you and Iceman indicated that with the superheat readings I was getting that the blockage was not in the plates, but likely further on.

The plates did not appear blocked. Had full nitrogen flow in each plate, both directions. Put a temporary valve at the outlet side of each plate to build the internal pressure up to about 20psi, opened the valve quickly to release pressure. Pressure dropped immediately. Don't know what else to do to check for plate blockage.

The problem with the freezer is not gone. It was there in the beginning with the five plates, and is still there now with just the 3 freezer plates.

Unfortunately did not take many measurements (dumb on my part) before separating freezer and refrigerator. Customer says that now with separate refrigeration compressor, the refrigerator plates are pulling down in about half the time.

The liquid separator was in place. Will be checking for blockage, other problems downstream of the cold plates today. Will try to verify that the liquid separator is installed correctly. According to the compressor serial number it is a low temperature unit. Will take all the readings you suggest and anything else I can.

Off to work....,

Kevin

[Intermez]

Forgot the most important question, is the anyway to check the suction accumulator, liquid separator for correction installation other than unbrazing it? I'm assuming that it won't be labeled, in and out, as life is never simple.

Kevin

[Peter_1]

Don't unbraze it, there mostly a stamped in and out
label on the accumulator.

Well, in fact blowing through is only to clean the system.
But you still can have a restriction, even when you have a flow through the plates.
A capillary tube is a big restriction and you stll have flow.
You can see on the pictures I posted the restriction but there's still a flow possible.

Soldering schradervalves and measuring pressure gives much more reliable information.

Therefore, the temperature readings I mentioned are important measurements you have to take.

And pressure readings on the different sections are then the second most important readings.

These are not the easy jobs but you can prove now that you know your job.

I haven't re-read all the posts of this thread but where have you measured the suction pressure?
I ask you this because if you should have taken it somewhere on the low pressure side of the compressor body and not on the service valve itself, then you also can have a restriction in the mesh filter installed inside the service valve (or in the service valve itself)
But no, you have a hermetic compressor which has no mesh on the inlet but there's still the servicevalve. But it's good to know that this could have been also a possible restriction.

To look for a restriction in the accumulator: you need to solder a servicevalve at the entrance of it and compare this pressure against the pressure at the service valve on the compressor.

[Peter_1]

Now, your suction temperature at the compressor is 70F. If we take the 70F suction temperature minus the -19F, you have over 89 degrees of superheat added to the evaporator superheat of 7 degrees. That's 96 degrees of total superheat at the compressor. That's enough right there to make the compressor very hot.

It would be nice to know the suction pressure now. The suction pressure SHOULD be close the evaporator outlet pressure if nothing else is wrong. A little lower, but not much.

I quoted US Iceman because his comment is very important because we rely on your measurements and we develop a theory, a possible cause based on this figures you give us.
It's therefore very important that we understand each other very well and that you corretc us eventually if we say something wrong or different from what you have measured.

[US Iceman]

The problem with the freezer is not gone. It was there in the beginning with the five plates, and is still there now with just the 3 freezer plates.


Now we know something new! The problem was not probably related to the plates, but essentially the refrigeration system that the five plates were originally connected to.;)

Since two plates are now on a separate refrigeration system and working fine, the problem seems more associated to the actual refrigeration system used for the freezer plates.

It the problem is not a "mouse", I bet it is something left there from the previous service tech. Rubber or plastic plugs that may have been left in something and partially melted when brazing was done.:o :eek:

[Peter_1]

Rubber or plastic plugs that may have been left in something and partially melted when brazing was done.:o :eek:

This is something happened by myself.:eek:

[Intermez]

Here's what I did yesterday. Didn't stay too long as it was on my own time. After reading all of your comments and thinking about it for a while, I guess the only way to determine if there is a blockage between the plate outlet and the suction port is to make simultaneous pressure measurents at the two points.

My assumption is that during startup with a cool compressor, is this is when the flow rates through the suction side are the greatest. I first took simultaneous measurments between the inlet side of the dryer (service port already there) and the suction port. The liquid accumulator is between these two points. I also opened the TEV wide open to get the greatest flow rates that I could (higher flow should mean higher pressure drops). I saw only 1 to 1.5 psi drop from the dryer inlet to the suction port. I did this for about 5 minutes, stopping again when the outlet temp reached 225F. My conclusion no blockage in dryer or accumulator. Do you guys agree with this?

Next I did simultaneous pressuren measurements between the plate outlet and the suction port. TEV wide open. Here's the series of measurments as the system started to pull down, again over about a 5 min. period.

EVAP Suction
Out Port
Press. Press.

15 16
13.5 15
13 14
11 12
10 11
9 10
8.5 9.5

All readings in PSI. Sopped again when discharge temp reached 225F. ( Don't like the idea of just letting the system run to let it stabalize, ignoring discharge temp as Peter suggested. From everything so far it think I'd fry the compressor because of very low ***** flow). Suction port temps were high starting around 88F dropping to 81F during the above. Conclusion, no blockage between plate outlet and suction port??

This is all I had time to do, will continue with your suggestions on Monday, back through the plates to the TEV. Will also try to take all the measurements suggested.

Many thanks, Kevin

[Intermez]

For some reason the table of pressure measurements and the headings for them didn't come out correctly on the post. The first column of numbers, starting at 15 and dropping to 8.5, are the suction port pressures. The numbers immediately to their right, starting at 16, dropping to 9.5, are the plate outlet temps.

Kevin

[Intermez]

D****, previous post, not plate outlet temps., plate outlet pressures!

I need to relax!

[US Iceman]

I also opened the TEV wide open to get the greatest flow rates that I could...


If I can make a suggestion... Do not adjust the TXV everytime you do something, please. Just because it has an adjustment stem on it does not mean turn the stem.

This is a very common mistake that people continue to make. They assume if the system is not cooling properly, it either has to be low on refrigerant or the TXV needs to be adjusted. The TXV should be adjusted at full load at normal operating conditions. Once the superheat is reasonable, Leave the valve alone.

I don't seem to remember any mention of a suction line filter drier before. What exactly do you have installed in the suction line between the three remaining plates and the compressor suction service valve?

Right now I'm counting a; suction filter drier, an accumulator, and a liquid/suction heat exchanger. Is there anything else?

[Intermez]

Iceman,

I agree on adjusting the TEV. It is the last thing usually touch. Problem is this system is not operating normally and there's no way to adjust the superheat correctly with what appears to be low ***** flow.

Yes, there are three things between in the suction line after the plate outlet. Heat exchanger, filter-dryer, accumulator, in that order. The filter-dryer was only mentioned early on. I said that after I first tried to get the system going unsuccesfully the first things I changed were the liquid line and suction line filter driers.

THanks, Kevin

[Peter_1]

Just reading your post before I go to sleep (11:15 PM) and coming back from helping my wife. It was very busy today
I thought the same about the suction drier. You didn't speak about that before.
A suction drier is something that blocks sometimes, reason why they install 2 measuring points on it.

If it's a suction drier, in fact a filter, then there are normally 2 measuring points. I suppose tehre is no pressure drop over these 2 points.

Can you make pictures of the complete setup?

You will need to make temperature measurements at the inlet and outlet of each component, starting at the TEV inlet.
Somewhere, there must be a sudden temperature rise, otherwise there was something wrong explained in a previous post or we understood it wrong.

I've seen compressors running at more then 225°F for quit some time (in terms of days)
So don't be afraid to let it run for some longer time then you do now.
Otherwise, you never can measure temperatures, it need some time to stabilise.

Perhaps a little schematic with every component on it and the temperatures you have measured. Try also to measure pressure on every point where you can measure it.

[US Iceman]

I've seen compressors running at more then 225°F for quit some time (in terms of days)
So don't be afraid to let it run for some longer time then you do now.


I agree with Peter. 225°F is getting warm, but not too bad. Now if the temperature was reaching 270-300°F then I would start to be concerned.



You will need to make temperature measurements at the inlet and outlet of each component, starting at the TEV inlet.


Kevin, this is absolutely critical information to have for trouble-shooting purposes.

If you mentioned the suction filter drier before, I may have missed it or forgotten it during the on-going discussion. Sorry about that.

If the suction pressure loss is not to excessive, then we have to start looking at other things as well. It would be nice to have the respective pressures and temperatures at each component (inlet & outlet). This allows us to examine each component for relative performance we might expect to see.



Somewhere, there must be a sudden temperature rise,...


If the pressure loss is minimal, then I think this is the next area we have to investigate. The data will tell us which direction to look at closer.

Have you performed a pump down test of the compressor yet?

This is pretty simple. Jump out or bypass the low-pressure switch. Attach your compound gauge to the suction valve port on the compressor. Now close the suction valve all of the way, so that it closes off the suction line to the compressor.

The compressor should pump down into a decent vacuum within a minute or so. Say 25 in.Hg. Shut the compressor off.

If the suction valves in the compressor are OK, the suction pressure decreases fairly rapidly. If it takes quite a while to pull down the suction pressure in the compressor, the compressor pumping capacity may be in error (leaking rings or suction valves).

If the suction pressure increases very rapidly, the discharge valves are broken. If this pressure rise occurs after the compressor shuts off, you might hear a "hissing" sound. That's the discharge gas equalizing back to the suction pressure.

This is a very easy check to make as it only takes a few minutes.

[Intermez]

Will make a complete diagram today.

Pull down test: went from 50psi down to 21 in Hg within 1 min. Sat at 21inHg for next 5 min. Turned compressor off and after another 5 min reading still at 21inHg.

Thanks again guys for hanging in there with me. Off to put in more access ports.

Kevin

[US Iceman]

Kevin,

When you have the compressor running in a vacuum, you should only keep the compressor running for about 1 minute. If the compressor is going to pull a vacuum, it will do so rather quickly. Allowing the compressor to operate in a vacuum for 5 minutes serves no purpose.

I was trying to remember something you need to understand about hermetic motors running in a vaccum. Don't do this for very long.

The insulation resistance of the motor decreases quickly in a vacuum. prolonged operation in a vacuum can cause other probelms that may force you to change the compressor.

[The MG Pony]

some of the guys I know who use them as vac pumps have run them upwards of two days at max vacuum so they can tolerate the abuse apperantly, befor I never knew that. I use a low temp unit to vacuum out my play systems at home, till I can buy a rotory vane vac pump.

Any case 21"mg that seems rather high for a low temp unit.

[Intermez]

Thanks for the heads up on pull-down run time. Will not run longer than a minute in the future. Will get to the diagram tonite. Have some temperature measurements, will get more readings and give full report later.

Did find something interesting. Pressure drop from TEV outlet, through three plate runs, and measured at plate outlet is running about 5 psi. Seems a bit high dosen't it?

Will fill that in with more data on pressures and temps.

Kevin

[Intermez]

Latest:

Ran system trying to get it to stabalize. Discharge temperature kept rising. Stopped at 295F, no sign of slowing down.

Found that first plate of three appeared to have lost about 50% of its brine. Made me suspicious bacause of pressure drops through 3 plates I had found earlier (5psi). Easier to bypass this plate entirely than to do anything else.

Ran system with only second and third plates. Was able to get system to stabalize somewhat with discharge temperature about 260F. Ran this way for about 30 min. My camera died so can't attach diagram I drew (figures!). Below is a list of the components, starting at the compressor, through the HP side, TEV, LP side.... Numbers before and after each component are the temperature measurements going into and coming out of that component where I was able to measure. System was still pulling down somewhat so readings were not 100% stable.

80F-COMP-260F
250F-CONDENSOR-115F
115F-RECEIVER-110F (@165psi)
VALVE
109F-FIL/DRYER-107F
107F-30FT. 3/8 LINE-95F
95F-HEAT EXCHANGER-80F
VALVE (pressure here 163 psi)
------------INSIDE COLD BOX
70F-TXV- -5F (@3.5psi)
-5F-PLATE 1- -9F
-9F-PALTE 2- -10F (@1.5psi)
--------------OUTSIDE COLD BOX
20F-HEAT EXCHANGER-40F
40F-30 FT 7/8 LINE-65F
65F-FIL/DRYER-67F
68F-ACCUMULATOR-75F
80F-COMPRESSOR-260F (0 psi @ suction port)

Thoughts?

Thanks, Kevin

[US Iceman]

Kevin,

See notes below. My comments are in red, next to your original data. Everything looks OK until you get to the red areas.


80F-COMP-260F
250F-CONDENSOR-115F
115F-RECEIVER-110F (@165psi)
VALVE
109F-FIL/DRYER-107F
107F-30FT. 3/8 LINE-95F
95F-HEAT EXCHANGER-80F
VALVE (pressure here 163 psi)
------------INSIDE COLD BOX
70F-TXV- -5F (@3.5psi)
-5F-PLATE 1- -9F
-9F-PLATE 2- -10F (@1.5psi) (about 6 degrees of superheat)
--------------OUTSIDE COLD BOX
20F-HEAT EXCHANGER-40F (at this point you about 50 degrees of superheat!, 40F minus -10F)
40F-30 FT 7/8 LINE-65F (now you have an extra 25 degrees of seperheat!, 65F minus 40F)
65F-FIL/DRYER-67F ( 2 more degrees of superheat)
68F-ACCUMULATOR-75F ( 10 more degrees of superheat)
80F-COMPRESSOR-260F (0 psi @ suction port) (+ 5 more degrees of superheat)

Adding up the numbers we have 6+50+25+2+10+5=98 degrees total. If we adjust this for pressure losses we 100 degrees of total suction superheat being added!!:eek: (80F at the compressor minus the saturation temperature at 0 psig = -20F = 80F minus -20 = 100 degrees.

That's why the compressor is hot!

The suction pressure loss does not look too bad, but the superheat is not at all helpful.:mad: :mad:

The superheat looks OK until you get outside of the box. Then somehow, when you are leaving the second plate and getting outside of the cold room you are adding about 30 degrees of superheat. (20F - -10F = 30 degrees). That's way too much! Six degrees of this came from the plates. Then to top it off, the suction heat exchanger is adding another 20 degrees. The two of these equal half of the total!

Does any of the suction line have insulation on it?

Is the suction line outdoors in the sun... Exposed?

Does the accumulator have the liquid line connected to it with seperate connections? Or, does the suciton line come into and leave the accumulator only? Does the accumulator have four connections or two?

Somewhere between the outlet of the second plate and leaving the cold room, you have a major problem...

Pictures of the installation would be nice to have as well as a piping diagram.:o

[Peter_1]

Just joining again this thread, wasn't able to post sooner.
We finished today a job that normally had to be finshed yesterday. Problem: 3 hermetic units where 3 lines were swapped, even a suction with a liquid line.
Most of the lines were installed underground.

This is a general note for many 'IP-posters': if you're not used to work with psi and °F, then these posts takes much more time to read and to 'understand and translate' them, especially when most of the answering has to be done in the evening after a very busy day. So, most of the times, I stop reading these posts and try to concentrate on other postings.
But this problem is to interesting to let it go now.

See that there were some posts and USIceman answered them all.
A schematic should be very usefull and some pictures is of course the best solution.

USIceman already made the necesarry calculations and conclusions: like already said in my post of 19/08, I think you need to replace the line between last plate and compressor inlet.
But you can do this much moire easily and faster in soft 5/8 copper, 7/8 is in my opinion far too large. And remove the accumulator and the HE at once, you don't need these fancy tricks. The more unnecessary items you install, the more they're prone to failure. (Is thsi a correct expression :) ?)
It's also only 30 ft of 5/8 copper, installs fast and without a lot of soldering.

I also suggest that you desolder it direct from the last plate and look once with a light in the hole if the tube inside the hole hasn't collapsed like the picture I posted in one of the first posts.

What's seems important for me - but USIceman pointed already to this - is the sudden temperature rise after the last cold plate and before the entrance of the HE.
Then in the HE, there's also something wrong.
What about a defective HE where there's an internal bypass between low and high side?

USIceman, with the 4 connections suction accumulator, you're thinking about the type with a HE build into it?

[US Iceman]

Hi Peter,

Sorry to hear about the underground piping problem. I worked on a job similar to this. Some split units separate by a roof. The installer had the liquid lines crossed between the two condensing units. It was fun to watch the refrigerant move from one system to the next, before I found the problem.:rolleyes: It was even more fun to explain it to the owner of the firm that installed it.:D I have never seen someone get so mad!:p




USIceman, with the 4 connections suction accumulator, you're thinking about the type with a HE build into it?


That's it exactly Peter. If he has two heat exchangers adding heat to the suction line, that is almost two, too many, if you know what I mean.;)



The more unnecessary items you install, the more they're prone to failure. (Is this a correct expression :) ?)


Correct on both counts Peter.

The interesting thing is, with the 7/8" suction line he has almost 3.5 to 5 psi pressure loss. This seems very high, but for the time being, I think it is a minor problem.

I cannot see how he would have this much pressure loss in only 30 feet of tubing??? Especially for this low of a capacity system?

Sorry about all of the IP units Peter. I'm facing the same problem you have. I'm trying to help the guy out, and I still have work to do also. A sorry excuse I know.:o

[Intermez]

Thanks!!!

Question, could all the temperature readings along the suction side be explained by very low refrigerant flow? Wouldn't this account for all the temperature rise? Pressure readings just don't point me to a particular point of blockage. If the TEV is somehow limiting flow to a low value is it possible to still get a superheat reading of 6F? Just a thought.

Suction line is insulated completely except for the heat exchanger. Suction line is indoors. Accumulator is 2 port, suction side only, no liquid line heat exchanger in the accumulator. Remember also that these readings are not an instantaneous snap shot. It took 5 or 10 minutes to get them.

The heat exchanger is coming out. Question about heat exchangers: I agree that thermodynamically it dosen't gain anything, but 1) dosen't the higher suction line temperature after the heat exchanger reduce heat gain along a long suction line because it is so much below ambient? and 2) in a cold plate system doesn't the lower liquid temperature create more rapid plate pulldown? In a cold plate system people are interested in pull down times more than total energy usage it seems.

Will take some pics as soon as I get camera working. I agree with replacing the 7/8 line with 5/8 line, pain in the butt, due to routing of line, but it is the right thing to do. It's impossible to get a view into the plates without totally unmounting them. They're right up against a panel on the top side of the plates with rt. angle flare connections. Not even sure how to disconnect the lines without removing the plates......which I'll have to do anyway to put in 5/8 line now that I think of it.

Supper time, must go NOW according to wife.

Kevin

[US Iceman]

1) dosen't the higher suction line temperature after the heat exchanger reduce heat gain along a long suction line because it is so much below ambient? and,
2) in a cold plate system doesn't the lower liquid temperature create more rapid plate pulldown?


1) heat transfer wise, the lower TD would add less heat to the gas. So, in theory you are correct. I still don't think the ambient is adding this much heat, unless the suciton line goes through a VERY warm space.
2) Cold liquid does add capacity, which would reduce the pull down time.



I agree with replacing the 7/8 line with 5/8 line,...


Unless the suction line has a kink or blockage in it somewhere, I would stay with the large size. One thing that might be proven quickly by changing the line is to see if the system works any better. Normally I hate to recommend this, but then, since I can't see the system I'm down to trying things.:(

Earlier in another post you mentioned one of the plates had leaked the glycol out of it. Where did the glycol go?

At this point, pictures are badly needed .

[Peter_1]

On the picture I post now, you can see also a leak I had, the TIG welded seem was teared. The picture needs to be turned 90°
So mostly they leak due to the continuous expansion and shrinking of the ice.
A standing plate tears mostly somewhere against the floor, mostly through a very small leak.

This becomes a really s**y job.


in a cold plate system doesn't the lower liquid temperature create more rapid plate pulldown? In a cold plate system people are interested in pull down times more than total energy usage
Yes and no, lower liquid temperatures means indeed faster pull downs in case this subcooling was created by other means of the system itselves (additional cooler, the ground, lower outside temperatures,..)
But with a HE you expanded also the suction gass with the warm liquid - energy was transfered from one to teh otehr side - so, indeed less liquid must be circulated due to the higher enthalpy of it but on the other hand the compressor must pump a larger amount of expanded gas, so a smaller mass flow at suction side.

So, in my opinion, the first compensates the second and thermodynamically seen, you can't 'create energy' in a HE.

I once read a paper - and I have stored it somewhere on my computer - about the benefit of a HE where they calculated the savings.

Can someone provide me a link to the used TEV of Sporlan? Searched for it in teh weekend but didn't find it.

[Intermez]

But with a HE you expanded also the suction gass with the warm liquid - energy was transfered from one to teh otehr side - so, indeed less liquid must be circulated due to the higher enthalpy of it but on the other hand the compressor must pump a larger amount of expanded gas, so a smaller mass flow at suction side.

Trying to get the "quote" to work as you guys use it. Quote is the above in case it doesn't work.

Understand what you said, but will the compressor in the above situation work harder, pull more amps, and add energy to the system....allowing faster pulldowns? Not interested in creating energy for a free ride with a heat exchanger, but interested in getting more out of the compressor allowing faster pulldowns. Have you ever seen an analysis of pulldown times with/without a HE regardless of energy consumed by the system?

Parker/Sporlan page very out of date. Will look for specs/info on the TEV in system.

[Intermez]

Here are two links that you've probably already seen. The TEV is a GF-1Z that isin't specifically referenced. Unit is one ton, R-12 low temperature bulb charge.

http://www.sporlan.com/10-10.pdf
http://www.sporlan.com/210-60.pdf

Question: If there is a blockage somewhere in the suction side after the TEV why don't I see high pressure readings when I measure the pressure immediately after the TEV?

[US Iceman]

Here is a link to a very good source that one of our other members posted:

http://www.refrigeration-engineer.com/forums/showthread.php?t=5590

[frank]

Not interested in creating energy for a free ride with a heat exchanger

The first Law of Thermodynamics states that the amount of energy in any given thermodynamic system is constant. Energy cannot be created nor destroyed.

Energy is described as the ability to do work.

A heat exchanger just exchanges heat energy.

No free ride I'm afraid :)

[US Iceman]

Kevin,

To use the quotes, try this:

First type in... Left bracket then quote=Screen Name then right bracket

Type or copy the quote you wish to add here.

Then type in... Left bracket then /quote then right bracket

This is the syntax required. What you should end up with is between the brackets, including the brackets. Does that help?

[The MG Pony]

[ quote=Snarfawidget ] blah blah blah [ /quote ]

like that but with out any spaces inside the brackets. Or simply use the word buble thing up top that says "wrap in quotes" after high lighting the text to be quoted.

[Dan]

I once read a paper - and I have stored it somewhere on my computer - about the benefit of a HE where they calculated the savings.

Here's one that says a liquid suction heat exchanger does not improve COP.

http://www.irc.wisc.edu/file.php?id=49

To quote the conclusion of a tedious paper:

Even though the liquid-suction heat exchanger has a negative impact on system performance, the system does benefit from the heat exchanger by preventing vapor in the liquid line before the expansion valve. The system designer must thus be very careful in choosing when to install a liquid-suction heat exchanger in a refrigeration system.

What makes sense to me is that any heat gained in the suction line after the evaporator is wasted work. Thus, transferring as much as possible from the suction line to the liquid line is going to reduce ambient heat gain and improve COP.

[Intermez]

Thanks for the directions on using the "Quote" function.

Did some digging on heat exchangers. It seems the answer isin't so simple. See http://www.irc.wisc.edu/file.php?id=49
It seems that it all depends on the refrigerant used, mostly. Food for thought.

Kevin

[Peter_1]

Seems that this link isn't working.

[Intermez]

Peter,

Tried clicking on the lick a few times. It worked for me. It's a PDF file. Here's the link for their HTML version:

http://72.14.209.104/search?q=cache:4V3Lmrqg0oAJ:www.irc.wisc.edu/file.php%3Fid%3D49+refrigeration+heat+exchanger+cop&hl=en&gl=us&ct=clnk&cd=12

Hope this works, VERY long link.

[US Iceman]

Peter,

I think this is the report I sent to you earlier this year. It is probably the one you were thinking of.

PS. Kevin, what has been happening with the project? We went from a problem job to the pro's & con's of liquid/suction heat exchangers...

[Intermez]

Got sidetracked on another job. Working on putting in a temporary 5/8 line to bypass the 3/4 to see if that makes a difference. If that works.......then I'll have a least another day to make it permanent. You wouldn't beleive where the 3/4 is routed, but that's another story. Also laid my hands on another TEV, perhaps better (1/2 ton rather than 1 ton and externally equalized), that I'll try. I'm at the point of trying things to see if they make a difference. Another thing I thought of is that since the system was originally R12 with mineral oil, might have some kind of oil/wax mixture sitting in the plates that's causing a partial blockage. Just don't think it is this bacause the pressure drop isin't terrible. If the 5/8 line and other TEV don't do anything I'll try flushing the plates.

Question: If there is a blockage after the TEV somewhere, why don't I see bigger pressure drops on the suction side? Wouldn't I build up liquid before the blockage and see a temperature drop after it?

Thanks, Kevin

[The MG Pony]

why are some owners so frugaly inclined? By now I'd have had the system teared out and a new one put in, then sell the old one as parts.

[Peter_1]

why are some owners so frugaly inclined? By now I'd have had the system teared out and a new one put in, then sell the old one as parts.

Selling parts with probably a fault in it? And selling cold plates already used? It's already a small market for these systems.

And I also disagree with your way of solving this problem, there' most likely nothing wrong with all the plates nor the compressor. So why replace those?

There's somewhere a fault in the system that must be localised and repaired afterwards. That's all.

Replacing all the parts, well, everybody can repair this way everything.
I then even can repair this way a Rolls Royce Trent 500 jet engine.;)
This isn't the right way because your don't learn anything doing it this way.

These kind of problems, well you can learn so many of it.
Wonder why so few join this thread.

What does "frugaly inclined" means?

[US Iceman]

HI Peter,



What does "frugaly inclined" means?


A fancy way of saying someone is cheap, or will not spend money.



By now I'd have had the system teared out and a new one put in...


This is the difference between a good service tech and a parts changer. Anyone can change parts. Not very many can find the problem and then fix it correctly.



I then even can repair this way a Rolls Royce Trent 500 jet engine.;)


That's true Peter.:D I want to be a brain surgeon, but I cant find any spare parts to change.:p

The system Kevin is working on is one of those he will remember I'm sure. These are the type of problems that make a good service tech better.

[Peter_1]

The system Kevin is working on is one of those he will remember I'm sure. These are the type of problems that make a good service tech better.
"Voila" said the French tech.

[US Iceman]

Peter,

You are such a master of the languages!:D

[Intermez]

I hate to repair things by swap out. Peter....your suggestion I believe......change the 7/8 to 5/8 suction line bypassing all the "stuff". Unfortunately, I happen to agree with you in this case although the readings don't directly support it. The TEV, that's all my idea, will take full responsibility for that one. Compressor and plates, can't be there.....I hope.

[The MG Pony]

So do I but if time is important on a production system and as you said it was old to boot then seems like the logical choice. Over time I have learnt that after a point there is no reason to continue fixing it up. I've been interested to see the problem solved as well, but an old system that had issues be for hand well like I said thats me.

FYI I didn't say swap out I said flat out replace the whole lot, I'd re-assemble the old one just to figure it out, sell of what was worth any thing.

[Peter_1]

Over time I have learnt that after a point there is no reason to continue fixing it up. FYI I didn't say swap out I said flat out replace the whole lot, I'd re-assemble the old one just to figure it out, sell of what was worth any thing.

And what may be that point for you? Seems that searching too long or dmaking some efforts is the main reason.

For me, the decission to replace an item is when it can't be repaired or a repair will cost more then a new one.

"By now I'd have had the system teared out and a new one put in" is exactly what you said, teare it out.

So many replaces parts without knowing why they replace it. "We will change this part and we will see if it's beter, if not, then we will change another part and left the previous part of course and see if this helps"
I have to admit, that's the reason why I hate to service nowadays airconditioning, you have to replace a whole PCB, without knowing what defective part you're changing. On these PCB's, the part that's broken cost mostly not more then a few cents.
But it's the only way to solve the problem.

[Peter_1]

You said that the valve has a number 1 behind the type.
According to the Sporlan literature, this '1' means that you have a capacity of 1TR, or +/- 3500 Watt.

A 1.5 HP LBP gives +/- 1200 Watt at -20°C, so your present valve is far too large.

Isn't it possible that this valve was placed by the previous tech and that he had turned on the needle so many turns, trying to achieve an acceptable SH that he closed it almost completely?

But if this valve is turned almost completely in closed position, then there's no possibility that it can inject sufficient refrigerant.

You need at least a valve of 1/2 TR or +/- 1700 Watt.

But still the sudden Sh botters me and you have somewhere a point saying that the readings don't support the replacement of the suction line. There should be also an accompanying pressure drop which there isn't.:confused:
But a HE can add heat without changing the pressure.

[Intermez]

But if this valve is turned almost completely in closed position, then there's no possibility that it can inject sufficient refrigerant. You need at least a valve of 1/2 TR or +/- 1700 Watt.


The valve I have available is 1/2 ton, will work with 401B, and low temp bulb charge. It's externally equalized, just have to put in equalization connection. Should be trying it today.


But still the sudden Sh botters me and you have somewhere a point saying that the readings don't support the replacement of the suction line. There should be also an accompanying pressure drop which there isn't.:confused:
But a HE can add heat without changing the pressure

The heat exchanger is only adding around 20F to the total superheat of 100F. So I don't think this is the problem, surely not helping things thought. Customer said he will allow me to "do some playing" with the system after I get it working. Want to see the difference with/without HE. By the way, took Peter's suggestion and printed out a slightly edited version of this thread and gave it to the customer. He was VERY IMPRESSED. Good idea Peter!! Guess you're OK no matter what everyone else says.

[US Iceman]

The heat exchanger is only adding around 20F to the total superheat of 100F.


Yes but... The heat exchanger and whatever is happening between the last plate and the heat exchanger is contributing about half of the superheat that you have.



Guess you're OK no matter what everyone else says.


Peter is a great guy and I defy anyone to say otherwise.:D



But still the sudden Sh botters me and you have somewhere a point saying that the readings don't support the replacement of the suction line. There should be also an accompanying pressure drop which there isn't.:confused:


This is the part of the problem I don't like. Pictures would really help for us to see what is going on. The data provided supports Peter's comment above quite well.

[The MG Pony]

And what may be that point for you? Seems that searching too long or dmaking some efforts is the main reason.

For me, the decission to replace an item is when it can't be repaired or a repair will cost more then a new one.

"By now I'd have had the system teared out and a new one put in" is exactly what you said, teare it out.

So many replaces parts without knowing why they replace it. "We will change this part and we will see if it's beter, if not, then we will change another part and left the previous part of course and see if this helps"
I have to admit, that's the reason why I hate to service nowadays airconditioning, you have to replace a whole PCB, without knowing what defective part you're changing. On these PCB's, the part that's broken cost mostly not more then a few cents.
But it's the only way to solve the problem.

No I do not do that, I replace total system and log it very well, so next time it needs work there is no guessing you read the log you know the exact age of the parts last opperation don, I am very neurotic about having things tightly organised and loged

[Peter_1]

No I do not do that, I replace total system and log it very well, so next time it needs work there is no guessing you read the log you know the exact age of the parts last opperation don, I am very neurotic about having things tightly organised and loged

Replacing the whole system just for a faulty TEV? Even better!

Keepings logs, running parameters and a sheet of the used material is of course very good, it's even mandatory in Belgium to do this.
Each intervention on the system must be clearly described in the same booklet and when you had a refrigerant loss, then you must describe where, reason and what you have done to prevent it happens again.

But that's not my point.

Nevertheless, you have your way to solve a problem, I have mine.
And there must be a difference, otherwise there should be no competition.

But, we still have a system functioning not properly that needs to be repaired. ;)

[US Iceman]

Replacing the whole system just for a faulty TEV? Even better!


This is just too funny.:D :D

And to think... I wasted all of those years sitting in school and listening to the old guys trying to tell me something.

I have not laughed that hard in a while!

[The MG Pony]

This is just too funny.:D :D

And to think... I wasted all of those years sitting in school and listening to the old guys trying to tell me something.

I have not laughed that hard in a while!


Lol now come on now, if it where this simple on the system in question I'd imagine he'd be don by now, but long term issues?

I am indeed keen on seeing what the problem is my self.

(As for the old guys I spend nearly ever minute of the day chatting with them ;) when I can; how do you think I've learnt this much? I'm on a 2 year waiting list for my entry course to start)

[US Iceman]

...but long term issues?


Then Kevin will have a life long customer. He tried to fix the system without just changing parts, which by the way, owners begin to notice after the second or third attempt. It does not take them too long before they begin to see what kind of tech is working on their system.

Once you loose your credibility with them, you could solve the problem the next day, and they will think you are guessing again.

Ripping out systems to "fix" problems is an easy way out. I hope the school you go to, does not condone this type of ethic?

[The MG Pony]

you all seem to be jumping to conclusions about my methodology, I would not resort to that right off and oft take times to work away the problem and oft do (Only on computers currently) but if the system has a history of issues and has an odd one then one must consider upgrading. I have a system on my bench in such a state I have worked on it multiple times and have it repaired and this is the 5thed time it needs work (More to it then just that but I'll leave the life story out of it) so I will recommend it is time for them to get a new one. that's what I was stating about this since he said it was having issues be for and if it is a time critical job.

Ripping out and replacing IS NOT THE DEFAULT! you all seemed to assume this is what I was saying when I wasn't.

We all have our own methodologies of doing things (and judging by the loyal customer base for Computer work I have I must be doing some thing right)

either I said it wrong or you miss understood either way we are all way off base as to the thread topic.

[Peter_1]

In the computer repairs, it's of course something different:
1. it's impossible to pinpoint the faulty piece on a PCB, and even if it should be possible, these pieces can't be found.
2. PCB's and all replacement parts are rather cheap, very cheap compared to pieces in refrigeration.
3. These replacements parts are made to replace, not to repair
4. Swapping pieces in a computer takes sometimes less then a minute. Removing a HE is a work of hours.

If it's not the default, well, I only can agree with you.

Perhaps I misunderstood you, but you must be aware that things can be understood different from what you mean, especially by those where English isn't there mother-tongue. :D

[chilly]

Not to familiar with this system at all guys.
But from a layman s point of view I would at this stage replace the tev and orrifice together (remove faulty tev from equation) also check cappacity of tev and orrifice is correct for system.
Ive pulled my hair out for daus before now because an engineer before me changed the tev for the size he happened to have in the van. (different to the one required)

Also I dont know the system but is their any way to reduce the load in order to test the system?

Has the load changed in recent times and is now too great for the system to opperate.

One last thing R49i is the replacement i use, Maybe the replacement gas your using is the problem, Perhaps try another replacement gas that is a better drop in.

Hope some of that is of use.

[US Iceman]

MG Pony,

Well, English is my native language and I understood you to say,



By now I'd have had the system teared out and a new one put in...


If we assumed too much, then why did you suggest tearing out the system as your second post to this thread?

If I'm coming across too harsh, I aplogize in advance for that, but I do not like the suggestion of tearing out systems, just because the problems are too diffficult to solve.

The important part of this (besides fixing the system) is to keep the owner fully aware of what you are doing to the system.

It is better to explain to the customer you are having some difficulty in finding the problem and then proceed to solve the issues. Most of them will appreciate the honesty and the willingness to carefully review the system before spending money on various parts.

One of the hardest things to learn when you are getting started in this business is... patience. Do not be in a big hurry to solve things.

[Peter_1]

The important part of this (besides fixing the system) is to keep the owner fully aware of what you are doing to the system.

It is better to explain to the customer you are having some difficulty in finding the problem and then proceed to solve the issues. Most of them will appreciate the honesty and the willingness to carefully review the system before spending money on various parts.

I would like to add USIceman: I allways explain my customers what I'm doin and why I'm doing something.
When I'm not sure it's reapaired for 100%, then I also tell client that he can expect troubles and try to predict what troubles we could expect.
Example: there was moisture in the system and the TEV was blocked. I replace the dryer but I tell the client that he has to monitor the sight glassand that the problem can come back.

I learned through the years that if you lie or don't tell everything, that everything will be thrown sooner or later in you face if truth comes above water or another tech comes on site and tells the customer his vision of the problem.

If a customer doesn't or won't understand that a problem can't allways immediately be fixed and that it can take some time before it's fixed, well, then I have happily the opportunity to walk away and he never had to come back to me.

That's the advantage of having too many work ;)

I once had a client who called me at 05 AM on a Sunday morning (in fact night for me :) )
I hadn't hear the phone and the answering machine took up the line in the office.

He made a second call around 06 AM and we heard someone giving an explanation.
So, I thought, I will see when I wake up at 08:00 AM.

At 07 Am, a 3th call and shouting realy loud through the telephone. I stood up and listened to the recorded tape: that this wasn't the proper way of servicing, that his coldroom already had problems since Thursday(!!!) and that it now on a Sunday morning completely had stopped and it was full of meat.

So I decided to go, I was anyway ready to start my Sunday with a croissant.

I told my wife that I should go first to help him before giving him my view and return with the croissanst so that we could eat together.

I entered at 07:20 his shop and he told me something like: "Well, you came walking I suppose, it's more then 2 hours I called you. You can see that' my fridge will be arranged within minutes " I stood their with my toolcase in my hand and in the other the doorknob and replied "Repeat that once again and I will even not place my toolbox on the ground for you. You can shout to your wife like a dog but not to me. If you don't appologise, then I will leave immediately"

His wife appologised for him and I repaired his coldroom. He's still a client but his attitude is changed since then.

[US Iceman]

I allways explain my customers what I'm doing and why I'm doing something.
When I'm not sure it's repaired for 100%, then I also tell client that he can expect troubles and try to predict what troubles we could expect.


Well said.

This is the reason why I also believe this...



I learned through the years that if you lie or don't tell everything, that everything will be thrown sooner or later in you face if truth comes above water or another tech comes on site and tells the customer his vision of the problem.


This is not the type of advertising you want for your reputation...to have people talking about you badly.

I once had a person similar to Peter's story (I'm sure everyone has a story like this;) ). He called at midnight with problems on an ice cream case. He knew about the problem at 6PM, but waited until midnight (after he quit trying to fix it himself??). I told him I could be there early in the morning (sunday morning again).

When I arrived, there was another service tech working on the system. He called every company until someone came right out.

He screamed and cursed at me and said it was my fault! I said OK, sorry you feel that way, and good luck with the new tech and went back home to enjoy the day.

Yes, we are off the topic, but these lessons can be just as valuable as learning refrigeration.

[The MG Pony]

Most of them will appreciate the honesty and the willingness to carefully review the system before spending money on various parts.

That would be my first operation would be to solve it, how ever the mentality of this area I live in they'd be at this point wanting it to work, hence by several weeks of looking and geting no where then I'd replace the whole system given that they said it was having issues befor hand.

Then I'd rebuild it at Home and find the problem, becuase I would like to know, but it is what the person wants. It is great the guy wants the old system repaired that is very rare now days (Or at least so it seems in thees parts again)

for some reason I thought this was a time criticle job. and when dealing with old systems with a history of having issues (This is what I got the jist of) it is best to properly build a very well documented one that will give years of truble free service. As the old dock saying goes: you can only patch the haul so many times befor your in a paper boat.

[The MG Pony]

I would not ever lie, that defeats the whole reason to talk, if the info you give is not right then best not waste the air to say it is my saying, no idea how we got on that line of thought, this is what I do, I all ways explain why and what in any field it is the only right thing to do.

Good business is repeat business, and honesty, quality and precision should all ways be the only acceptable out come, and so far I have maintained that stance and methodology and all ways will

[Peter_1]

Any news on this one?

[US Iceman]

Peter, it seems we have lost our little project???:confused:

[Sledge]

Hi

It is 12:30 am and I cant read to the end of the thread, not certain if anyone else has posted this...

I have in front of me a publication from Honeywell on retrofitting from R12 to MP66. They state that excessive discharge temperatures and capacity reduction may occur in situations where you have high compression ratios. It can be seen at honeywell website

I am also looking at an article entitled
Compressor overheating Todays's Most Serious Field Problem from Aug 1981 RSC. Without reprinting it here, the author explains the impact of a LL to suction heat exchanger. Adding such a HE to a system with insulated suction line contributes to compressor failures by elevating suction return temperatures.
There is a direct correlation between the discharge temperature and the return gas temperature. The author recommends installation of a desuperheating valve within 6 feet of the compressor.

I am looking at this as a problem of refrigerants gone bad to worse.

If this is a copeland semi-hermetic, I would add cooling water coil around compressor body, or change to different refrigerant. My research is showing that the latest and greatest drop in refrigerant to replace R12, compatible with all oils is RS24. The only issue with it is low temp applications require PE oil, but you dont have to be anal about it. The PT chart for it is almost identical to R12 and minimal glide.

I am going to use this refrigerant on all my changeovers. I would suggest trying it here.

[Peter_1]

Can you provide us a link to this Honeywell website?
Couldn't find it.

There is a direct correlation between the discharge temperature and the return gas temperature. This is of course true because but where is the big Sh coming from.

What does the author mean with a 'de-superheating valve'?
I could imagine what he's trying to explain but how must this be doen in practice? You simply can't inject refrigerant in the sution line without taking certain precautions.

If the system is well designed, then you don't need fancy tricks to protect the compressor from high discharge temperatures. http://www.refrigeration-engineer.com/forums/showthread.php?t=5203

[Intermez]

Sorry everyone, the thread is not lost. Was called away due to an unexpected death in the family.

Here's where things are at. Replaced the 7/8 suction line with 5/8 with new insulation. Removed the heat exchanger and suction accumulator. New liquid line and suction line filter/dryers installed. New TEV (externally equalized). I do not have a complete set of readings as of yet but will get them today.

I am now able to keep the system running without it going supernova.

With the factory TEV super heat setting I was seeing about 15F of superheat which gradually decreased to around 2F as the system ran for the first 20 minutes, however I was still seeing the discharge temperature climbing up to about 240F (and still climbing) when I shut things down. Suction temperature at the compressor was around 60F. To me, the problem is still there. At this point I assumed that the large amount of superheat added by the suction line could only be due to low flow.

I decided to forget about the superheat setting at the plate outlet. Decided instead to set the superheat only by the superheat at the suction inlet at the compressor. Took a stab, opened up the TEV by 1.5 turns. Suction superheat at compressor now around 20F. Discharge temperature around 210F. At the plate outlet the readings now are: 6psi and temperature of -13F. This equates to -7F superheat at the plate outlet (negative superheat). This was after 30 minutes of running. Plates seem to be pulling down nicely, but this is where I stopped. Will get a detailed set of readings today.

Is this at all normal in cold plate operation? Obviously there is liquid evaporation in the suction line, but I still have low temps at the plate outlet. The amount of heat added by the suction line is down considerably, running about 30F (not the 100F I was seeing before). I'm not yet sure what happens with these settings as the plates pull down. I also don't know yet if the suction superheat will remain stable as the plates pull down (worried about liquid slugging). Should find out today.

Thanks again guys!, Kevin

[kevinmcggg]

possibly not enough refrigerant to do the job?

[Intermez]

PROBLEM SOLVED!!!!!

Peter and Iceman and everyone else, thanks for all your help! I know you all thought I was nuts with the symptons/readings I was getting, but they were real.

It was the contactor. The relay/contactor on this system was a solid state one, not a mechanical one. One of the first things I checked on this system was the voltage at the compressor at startup when the current is the highest. It was around 210 volts, just fine. What was happening is that the solid state contactor was heating up and after 5 or 10 minutes the voltage at the compressor had dropped to 190 volts. All AC motors generate excess heat when operating at lower than normal voltage. This excess heat is what was causing the high exhaust temps. Replaced the contactor with a good old mechanical type and can now adjust things as they should be. It's now working fine. Will have to do some fine tuning but everything is now operating as it should.

By the way, if any of you recall somewhere near the beginning of this thing, I mentioned that the system had both a temperature and suction pressure shut down for some reason. Don't like a temperature shutdown, so I disabled it by setting it to -10F. The system shutdown because with a lot of tweaking I got it down to -10F. When it shut down, I figured I had locked up the compressor, as I had totally forgot about the temp shutdown. Started taking voltage readings to figure out what was going on. That's when I discovered the low voltage problem. So I can take no credit for solving this, it was just dumb luck!

Thanks again everyone, Kevin

[Peter_1]

Kevin, congratulations.
I should never had thought on this propable cause.
This was really a very, very difficult one.
I think that you have learned a lot with this s...y thing.
And this is also something I will try never to forget.

I was wrong with my diagnosis.

A SSR is indeed not the best option for this kind of application. I only use a SSR when there's a need for very fast switching.

Anyway, these service calls will make you every time a better tech then already are.;)

[US Iceman]

Well, well... If someone were to say we got our knickers in a knot over this project I would have to agree.

It still doesn't explain the high superheat out of the last plate and through the wall though:confused: .

If it works, I am not going to kick a sleeping dog.;)

In any event, I hope all of this was worth something to you Kevin.



Anyway, these service calls will make you every time a better tech then already are.;)


Amen brother...

[frank]

If it works, I am not going to kick a sleeping dog.;)

Should this be posted in the other thread :D ?

[US Iceman]

I'll add that minor contribution to the other thread Frank.

Do you want to guess how many kicks it takes?

[Intermez]

Thanks again everyone!



It still doesn't explain the high superheat out of the last plate and through the wall though:confused: .



This problem and all the other weird readings were because of low ***** flow, not enough gas flow to keep the temperatures from rising quickly.......just the way I had to set the TEV to keep things running without the compressor temp going over 250F. All the readings make sense now that I have a compressor that is acting normally. Oh yeah, remember the low ultimate suction with no flow....I'll bet it is higher now that the compressor is running with full voltage.

Finally :p , Enough school for now, Kevin

[US Iceman]

This problem and all the other weird readings were because of low ***** flow, not enough gas flow to keep the temperatures from rising quickly


I'm not sure if I buy that. The contactor had nothing to do with the mass flow, other than the fact the compressor shut off.

50 degrees of superheat increase within a few feet of pipe is not an answer of low mass flow.

But, if you are happy with the results then I won't argue about it.

[dirk]

it seems the compressor capacity is insufficient or compressor inefficient.

[dirk]

Still sounds like a compressor capacity problem